1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to spindle motors for disk drives and disk drive that use such spindle motors.
2. Description of the Prior Art
A typical hard disk drive includes a head disk assembly (“HDA”) and a printed circuit board assembly (“PCBA”). The HDA includes at least one magnetic disk (“disk”), a spindle motor for rotating the disk, and a head stack assembly (“HSA”) that includes a read/write head with at least one transducer for reading and writing data. The HSA is controllably positioned by a servo system in order to read or write information from or to particular tracks on the disk. The typical HSA has three primary portions: (1) an actuator assembly that moves in response to the servo control system; (2) a head gimbal assembly (“HGA”) that extends from the actuator assembly and biases the head toward the disk; and (3) a flex cable assembly that provides an electrical interconnect with minimal constraint on movement.
A typical HGA includes a load beam, a gimbal attached to an end of the load beam, and a head attached to the gimbal. The load beam has a spring function that provides a “gram load” biasing force and a hinge function that permits the head to follow the surface contour of the spinning disk. The load beam has an actuator end that connects to the actuator arm and a gimbal end that connects to the gimbal that carries the head and transmits the gram load biasing force to the head to “load” the head against the disk. A rapidly spinning disk develops a laminar airflow above its surface that lifts the head away from the disk in opposition to the gram load biasing force. The head is said to be “flying” over the disk when in this state.
Within the HDA, the spindle motor rotates the disk or disks, which are the media to and from which the data signals are transmitted via the read write/head on the gimbal attached to the load beam. The transfer rate of the data signals is a function of rotational speed of the spindle motor; the faster the rotational speed, the higher the transfer rate. A spindle motor is essentially an electromagnetic device in which the electromagnetic poles of a stator are switched on & off in a given sequence to drive a hub or a shaft in rotation, the hub including a permanent magnetic ring.
Hard disk drives are susceptible to non-operational shocks (shock events occurring when the drive is not in operation) due to both normal and unintended rough handling, both during the manufacture of the drives (during the disk clamp installation process or during qualification testing, for example) and at the hands of end users. Such non-operational shocks may damage the drive by causing permanent deformation of bearings within the spindle motor. There is a need, therefore, for spindle motors and disk drives incorporating such spindle motors that are configured to withstand non-operational and operational shocks of a relatively great magnitude.
As the storage capacity and speed of modem disk drives continues to increase, a number of design and manufacturing challenges have emerged. One such challenge encountered by magnetic hard disk drive designers and manufacturers is to reduce acoustic noise. Acoustic noise is measured according to such standards as the European ISO acoustic standard, the permissible acoustic threshold of which continues to be lowered. Arguably more important, however, is that acoustic noise is often measured by the consumer's own perception. Indeed, consumers tend to form an association between acoustic noise and quality, in that loud drives (those that generate excessive acoustic noise) are perceived to be of lower quality than like performing but quieter drives. Finally, acoustic noise is used throughout the industry as benchmark qualification against competitors' products. Shock events of a high magnitude may also cause increased acoustic noise emanating from even slightly deformed and damaged bearings. There is a continuing need, therefore, to develop and bring to market disk drives that emit little acoustic noise.
Another design challenge that has emerged is that of resonances within the spindle motor disk stack assembly. Such resonances degrade the drive's ability to remain on track during write operations, among other ill effects. Therefore, there is also a need to develop disk drives in which such resonances are sufficiently attenuated so as to enable compensation thereof by the disk's servo system.